Phase II/III, randomized, placebo-controlled, two-armed, comparison AIDS Clinical Trial Group (ACTG) study. Two important criteria for establishing an AIDS diagnosis in those with HIV infection are the development of an opportunistic infection and the presence of recurrent or multiple serious bacterial infections. Pneumocystis carinii pneumonia (PCP) is the most common opportunistic infection reported in children and has accounted for >40% of all AIDS defining illnesses in this age group. The primary aims of the study are to determine the comparability of azithromycin plus atovaquone to trimethoprim/sulfamethoxazole (TMP/SMX) in the prevention of serious bacterial infections and to determine and compare the long-term safety and tolerance of micronized atovaquone plus azithromycin versus TMP/SMX.